What is IP warming?
IP warming is the gradual building of trust with receiving mail providers when you start sending from a new IP address or a new domain. You begin with small volumes to your most engaged recipients and increase step by step over a period of two to six weeks. Anyone who instead sends thousands of messages straight away from an address with no history behaves exactly like a spammer, and is treated as one.
Why providers react this way
A receiving server does not know you. All it sees is an IP address and a domain with no past that suddenly offers a lot of mail. Spammers do precisely that: a fresh server, a new domain, send as much as possible before anyone notices. Providers have one answer to it: anything that is new and starts big goes to the spam folder or gets slowed down until they know more. Warming is how you give them that "more": a history of messages that are accepted, opened and not reported.
How it works
You start with a small number of messages a day to the people who open and click your mail most often. Those positive signals build reputation. Then you raise the volume in steps, for example every day or every few days, while watching bounces, complaints and delays. If those stay low, you may continue. If they rise, you hold the volume steady for a few days before going further.
A schedule for a medium-sized sender might look like this: a few hundred messages on day one, around a thousand a day after a week, a few thousand after two weeks, and the full volume only after three to four weeks. The exact numbers depend on what you eventually send and on how recipients respond. It is not a setting you switch on but a schedule you follow.
Why your best recipients first
Because the first messages carry the most weight. If you start with your oldest, dormant addresses, you immediately build a bad reputation that will trouble you for weeks: many bounces, few opens, perhaps a few complaints. If you start with customers who ordered last month or opened your last three newsletters, the provider sees a sender whose mail is wanted. Segmenting a list on recent activity is therefore the first step of every warming schedule; how to do that is explained under list segmentation.
When it applies
- A new sending domain or subdomain. Reputation is partly tied to the domain, not only to the IP address.
- A switch to another provider. Your old reputation does not move with you. Anyone who switches on Monday and sends the full newsletter on Tuesday sees it in the figures straight away.
- A long period without sending. Reputation fades. A newsletter that reappears after eight months of silence is, to the provider, a new sender.
- A big jump in volume. Going from two thousand to twenty thousand messages a month is just as suspicious to a filter as a new address.
How to tell that warming was skipped
Your first big send from a new domain or platform arrives noticeably badly, while small test messages before it landed perfectly in the inbox. In the logs you see many temporary errors (codes starting with a 4) and delays of hours at one or two large providers. That is throttling: the provider is not saying no, but "not so fast". If you keep pushing, it becomes a no.
What it does not replace
Correct authentication and a clean list. Warming with a bad list is building trust you immediately tear down again. First get SPF, DKIM and DMARC in order and remove hard bounces, and only then start the schedule.
When you do not have to do it yourself
If you send modest volumes through a shared IP pool with an established reputation, your messages ride on that history and warming the IP address is not your concern. Your domain still has to build a history of its own, but at small volumes that happens by itself. At 2Mail, IP warm-up with personal follow-up is part of the service: the relay sends at a fixed pace tuned to each large mailbox provider, you build up the volume step by step yourself with staggered sending in batches, and temporary errors are retried automatically. How that works in practice is described on the deliverability page.
Frequently asked questions
How long does IP warming take?
A week or two at modest volumes. At tens of thousands of messages a day, more like four to six weeks. The recipients set the pace, not your calendar.
Do I need to warm up if I only send order confirmations?
Usually less strictly: transactional mail is opened readily and rarely reported, and the volume grows naturally with your orders. A new domain still starts with no history, so avoid a big catch-up send on day one.
Can I speed up warming?
Only by choosing better recipients, not by sending more. A day on which you send too much costs you more time than a day on which you send too little.